An elongated wedge assembly as shown in FIG. 1A (Prior Art) is a well known clamping fastener currently used, where two end sections and a mid-section are shaped as "wedges". In particular, U.S. Pat. No. 4,775,260 invented by Kecmer and entitled "Printed Circuit Board Mounting Apparatus." shows these features. By forcing the two end sections to move towards each other by an axial force applied by a screw assembly, the wedge sections "climb" ramp elements of the mid section, thus creating a "wedging" action between the PCB and enclosure by an expansive force. Limitations of such a "wedging" assembly include i) potential instability due to misalignment of parts and ii) excessive wear of the individual wedge component parts due to end sections of this wedge assembly having a translation movement which inherently posits a frictional forces between wedge sections and the enclosure itself; and iii) decreased relative clamping force in comparison to the instant invention due to the instant invention having greater degree of mutual surface contact area between the clamping assembly and the enclosure.
Other prior wedging assemblies include have addressed thermal clamping measures by use of monolithic wedge elements for maintenance of a proper thermal path. For example, see U.S. Pat. No. 4,971,570 by Tolle et al. entitled "Wedge Clamp Thermal Connector" and U.S. Pat. No. 5,382,175 by Kunkel entitled "Thermal Core Wedge Clamp." These devices have the same limitations as listed above and additionally do not include a torque limiting device in a screw head assembly for applying a tightening torque for transmission of an expansion force by the wedging/clamping assembly and the enclosure as does the instant invention.
The amount of expansion force a PCB fastener can maintain is limited by the screw torque handling capabilities. The use of a torque limiter is shown in the U.S. Pat. No. 4,775,260 where a safety jaw coupling is used. Due to space limitations, the compression spring of this teaching's device can provide only limited torque handling capabilities before being overstressed. Variations in the fabrication of the springs together with the manufacturing of very minute teeth out of hardened steel make this device unreliable, viz. decoupling torque can vary as much as 200% from one device to another. To overcome this limitation and bring about a device that closely limits the amount of torque a clamping fastener can develop for accurate repetitiveness of torque applied to such a fastener over the course of maintenance work for the PCB, the instant invention solves this problem as well.